Pressure Sensitive Bypass Defrost System

ABSTRACT

A heat recovery ventilator defrost system utilizing a bypass section which supplies warm air in both channels of the heat exchanger to accelerate defrost, continue some ventilation of stale warm air, and recirculate a portion of the stale air flow, so as to warm incoming cold fresh air. When the system is in defrost mode, warm exhaust air to be expelled enters an exhaust inlet port and into an exhaust plenum. Because the air being exhausted (by way of the exhaust fan) through the exhaust plenum is under a positive pressure, the stale air will still be sucked out through exhaust passageway into discharge plenum, but also through the passive non-motorized bypass section into inlet plenum. Further, because fresh air continues to be drawn into inlet plenum, due to the positive pressure, the warm stale air which has passed through the bypass section (flap) into inlet plenum is then drawn through the heat exchanger along the inlet passageway into supply plenum, and out through supply port into the enclosure or dwelling. In this way, the heat recovery ventilators defrost system of the present invention supplies warm air in both channels of the heat exchanger.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to air exchange ventilators for admitting fresh air into an enclosure while exhausting stale air. More particularly, this invention relates to a defrost arrangement for air exchange ventilators which include a heat exchanger to extract heat from the stale air and transfer it to the incoming fresh air, and which introduces warm air in both channels of the heat exchanger to accelerate defrost, continue some ventilation of stale warm air, and recirculate a portion of the stale air flow at mild temperatures as opposed to the lower temperatures of incoming fresh air.

2. Description of the Related Art

Highly energy efficient buildings are generally designed to avoid uncontrolled intake and out-take of air. As some air exchange is necessary to remove stale air and replace it with fresh air, it is desirable in winter to first remove heat and or energy from the stale air and replace it with fresh air, and it is preferable to first remove heat and or energy from the stale air being exhausted to avoid losing this heat. A heat/energy recovery ventilator is therefore used for this purpose.

A heat recovery ventilator includes a heat exchanger with two discrete air passageways; one for stale air exhaust, and the other for fresh air supply. As the exhaust air passes out of the enclosure or building through the heat exchanger, it gives up its heat to the fresh supply air entering the enclosure through the heat exchanger. Accordingly, the heat is recovered in the ventilator during the ventilation process and hence the name, A heat recovery@ ventilator. Note: The heat exchangers performance is dependant on the difference in temperature and energy recovery unit works because of a difference in enthalpy between the two airstreams.

Problems ensue with heat recovery ventilators in situations where the fresh air supply is near or below freezing temperatures. During colder seasons, as the stale air generally contains moisture, once it passes up heat the moisture will freeze in the stale air exhaust passageway or on components in the heat recovery ventilator. Eventually, ice-build up will block the passageway, preventing or inhibiting the exhausting of stale air, or cross contamination due to flap leakage may occur; Balanced ventilation suggests that both incoming and outgoing flows are equal and that pressure drops created within the heat exchanger are higher on the fresh air channel because of its fluted passageway, thus preventing the flap from opening.

Different mechanisms have been proposed in order to defrost the ventilator, for example, as disclosed in Canadian Patent No. 2,059,195 and Canadian Patent No. 2,140,232. According to the latter, two actuators and respective valves or flaps are used to close the exhaust outlet and fresh supply air inlet. Stale air is thereby redirected to return back through the fresh supply air passageway to defrost the stale exhaust air passageway. This is carried out periodically, typically before the passageways totally freeze up. A drawback to this arrangement is the cost and complexity associated with utilizing two actuators each controlling separate valves or flaps.

The former patent suggests that instead of having two actuators, it is possible to prevent the cold supply infiltration inlet by diverting stale air exhaust back through the fresh supply air passages in the heat exchanger. While this does eliminate a valve or flap and an actuator, it does present its own problems. As the actuator and flaps are disposed adjacent the cold supply there is a possibility of their freezing, thereby rendering them inoperable. Furthermore, while the fresh air supply is closed stale air is recirculated.

Other problems inherent with conventional heat recovery ventilators is that, while such ventilators in a continuous operational mode, with both fans operating, to circulate air through the heat exchanger provides a balanced ventilation, during defrost mode, however, the fresh air intake motor shuts off to allow the stale air to warm up the heat exchanger, and such a shut off system can contribute to the depressurization within the dwelling. What is required is a heat recovery ventilator defrost system which introduces warm air in both channels of the heat exchanger to limit the depressurization and increase the efficiency of a defrost system.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved heat recovery ventilator defrost system utilizing a bypass section which supplies warm air in both channels of the heat exchanger to accelerate defrost, continue some ventilation of stale cold air, and recirculate a portion of the warm stale air flow to limit the depressurization effect, so as to maintain the heating capacity of the heat exchanger.

According to another object of the present invention, there is provided an improved heat recovery ventilator defrost system which utilizes a non-motorized bypass section for supplying warm air to both channels of the heat exchanger.

A still further object of the present invention is to provide an improved heat recovery ventilator defrost system which uses two independent air flows for defrosting of the heat exchanger.

A still further object of the present invention involves providing a means for protection against system failures. A malfunction that would have both motors operate continuously in wintertime would eventually produce frost build up in the stale air passageway of the heat recovery element, thus increasing the pressure drop that would in turn open the bypass section to let the warm stale air flow in the fresh air passageway to reheat the heat exchanger.

According to one aspect of the present invention, there is provided a heat recovery ventilator comprising a heat exchanger having discrete inlet and exhaust passageways extending therethrough for providing heat transfer and flow between respective fluids flowing along said inlet and said exhaust passageways, said inlet passageway providing fluid communication between an inlet plenum and a supply plenum, said exhaust passageway providing fluid communication between an exhaust plenum and an exhaust discharge plenum; and a bypass section positioned between said inlet plenum and said exhaust plenum, the bypass section being movable between a venting configuration, in which the bypass section is in a closed position for allowing fluid communication between the exhaust plenum and the exhaust discharge plenum, and a defrost configuration, in which the bypass section is in an open position and permits fluid communication between said inlet plenum and said exhaust plenum, in addition to allowing fluid communication between the exhaust plenum and the exhaust discharge plenum.

According to another aspect of the present invention, there is provided a heat recovery ventilator comprising a heat exchanger having discrete inlet and exhaust passageways extending therethrough for providing heat transfer and flow between respective fluids flowing along said inlet and said exhaust passageways, said inlet passageway providing fluid communication between an inlet plenum having an inlet port for admitting supply air into said inlet plenum and a supply plenum having a supply port for discharging supply air, said exhaust passageway providing fluid communication between an exhaust plenum having an exhaust inlet port and an exhaust discharge plenum, said exhaust discharge plenum having an exhaust port for discharging exhaust air from said exhaust discharge plenum; and a bypass section positioned between said inlet plenum and said exhaust plenum, the bypass section being movable between a venting configuration, in which the bypass section is in a closed position for allowing fluid communication between the exhaust plenum and the exhaust discharge plenum, and a defrost configuration, in which the bypass section is in an open position and permits fluid communication between said inlet plenum and said exhaust plenum, in addition to allowing fluid communication between the exhaust plenum and the exhaust discharge plenum.

Yet another aspect of the present invention provides for a heat recovery ventilator comprising a heat exchanger having discrete inlet and exhaust passageways extending therethrough for providing heat transfer and flow between respective fluids flowing along said inlet and said exhaust passageways, said inlet passageway providing fluid communication between an inlet plenum having an inlet port for admitting supply air into said inlet plenum and a supply plenum having a supply port for discharging supply air, said exhaust passageway providing fluid communication between an exhaust plenum having an exhaust inlet port and an exhaust discharge plenum, said exhaust discharge plenum having an exhaust port for discharging exhaust air from said exhaust discharge plenum; a supply fan mounted within the inlet plenum for augmenting fluid flow along said inlet passageway; an exhaust fan mounted within one of the exhaust plenum and the exhaust discharge plenum for augmenting fluid flow along the exhaust passageway; and a bypass section positioned between said inlet plenum and said exhaust plenum, the bypass section being movable between a venting configuration, in which the supply fan is turned on and the bypass section assumes a closed position for allowing fluid communication between the exhaust plenum and the exhaust discharge plenum, and a defrost configuration, in which the supply fan is turned off and the bypass section assumes an open position and permits fluid communication between said inlet plenum and said exhaust plenum, in addition to allowing fluid communication between the exhaust plenum and the exhaust discharge plenum.

The advantage of the present invention is that it provides an improved heat recovery ventilator defrost system utilizing a bypass section which supplies warm air in both channels of the heat exchanger to accelerate defrost, continue some ventilation of stale cold air, and recirculate a portion of the warm stale air flow to limit the depressurization effect, so as to maintain the heating capacity of the heat exchanger.

Yet another advantage of the present invention is that it provides an improved heat recovery ventilator defrost system which utilizes a non-motorized bypass section for supplying warm air to both channels of the heat exchanger.

A still further advantage of the present invention is that it provides an improved heat recovery ventilator defrost system which uses two independent air flows for defrosting of the heat exchanger.

A still further advantage of the present invention is that it provides a means for protection against system failures. A malfunction that would have both motors operate continuously in wintertime would eventually produce frost build up in the stale air passageway of the heat recovery element, thus increasing the pressure drop that would in turn open the bypass section to let the warm stale air flow in the fresh air passageway to reheat the heat exchanger.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a side perspective view, which illustrates the intake of fresh air and exhaust of stale air in a conventional air exchange ventilation system;

FIG. 2 is a side perspective view of one embodiment of the present invention, which illustrates the intake of fresh air and exhaust of stale air, and which illustrates the airflow of two independent air flows for defrosting of the heat exchanger; and

FIG. 3 is a diagram of an interior of a heat recovery ventilator according to the present invention in a ventilation mode;

FIG. 4 is a side view which illustrates the intake of fresh air and exhaust of stale air in a conventional air exchange ventilation system;

FIG. 5 is a side view which further illustrates the embodiment shown in FIG. 3, and which shows an interior of a heat recovery ventilator according to the present invention in a ventilation mode;

FIG. 6 is a side view which further illustrates the embodiment shown in FIG. 3, and which shows an interior of a heat recovery ventilator according to the present invention in a ventilation mode; and

FIG. 7 is a side view which further illustrates the embodiment shown in FIG. 3, and which shows an interior of a heat recovery ventilator according to the present invention in a ventilation mode.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a defrost arrangement for air exchange ventilators which includes a heat exchanger to extract heat from the stale air and transfer it to the incoming fresh air, and which introduces warm air in both channels of the heat exchanger to accelerate defrost, continue some ventilation of stale warm air, and recirculate a portion of the stale air flow at mild temperatures as opposed to the lower temperatures of incoming fresh air. In conventional systems, during the defrost mode the fresh air motor shuts off, and warm stale air is used to defrost the heat exchanger. This air is then totally expelled outdoors which can contributes to the depressurization within the dwelling or building. With reference to FIGS. 1 and 4, incoming fresh air is admitted into the air exchange system at (2) to flow through an inlet passageway (4), which is then passed through the heat exchanger (6), to flow (8) into an enclosure. Exhaust air to be discharged from the enclosure flows at (10) through the heat exchanger (6) to an outlet passageway (12) and out of the enclosure at (14).

In the present invention, the heat recovery ventilator utilizes a non-motorized bypass section (flap) to introduce warm air to both channels of the heat exchanger, so as to accelerate defrost, continue some ventilation of stale warm air, and recirculate a portion of the stale air flow, so as to warm incoming cold fresh air. In the present invention, because the stale air is under a positive pressure, the air being bypassed is being sucked back into the dwelling, thus reducing the net stale air exhausted to the outdoors. Thus, the present invention provides a highly effective defrost arrangement for air exchange ventilators which operates to provide extreme weather performance, and withstand extreme cold. During normal ventilation, the static pressure created by air moving through the fresh air passages in the heat exchanger creates more of a pressure drop than the strait air passages on the stale air side. Thus, this differential pressure is used to close off the bypass section (flap).

In one embodiment of the present invention and with reference to FIG. 2, a heat recovery ventilator 1 utilizes a non-motorized bypass section (flap) 42 to introduce warm air to both channels of the heat exchanger or heat exchanger 6 during defrost, in one air flow marked as 5 to warm one channel of the heat exchanger 6, and another independent air flow 7, which flows through the bypass section (flap) 42 to warm the other channel of the heat exchanger 6.

During defrost, and with further reference to FIGS. 3, 5, 6 and 7, at the heat exchanger of the heat recovery ventilator 1 is a heat exchanger 6 having an inlet passageway illustrated by arrow 20 and an exhaust passageway illustrated by arrow 36. To augment air flow along the inlet passageway 20 and exhaust passageway 36, an exhaust fan 54 may be mounted within an exhaust plenum 34, and a supply fan 60 may be mounted in an inlet plenum 24. Of course, providing such fans within the heat recovery ventilator 1 is desirable in order to make the heat recovery ventilator 1 a A stand alone@ unit. Preferably, these fans should be of similar capacity and may be arranged, if required, to share a common motor (not shown).

A housing (not shown) defines an exterior of the heat recovery ventilator 1, and it will be appreciated that the actual unit will have a front cover, which is not shown in the Figures so as to show its interior. The inlet passageway 20 and outlet passageway 36 allow heat transfer between respective fluids flowing there along without allowing co-mingling of the fluids. As is common with air to air heat exchangers, the heat exchanger 6 may comprise a plurality of individual passageways therein (not shown), which allows fluids flowing in the inlet passageway 20 and exhaust passageway 36 and through the heat exchanger 6 a greater surface area with which to enhance heat transfer. The inlet passageway provides fluid communication between the inlet plenum 24 and supply plenum 26. The outlet passageway provides fluid communication between the exhaust plenum 34 and discharge plenum 40. The inlet plenum 24 has an intake port 30 for admitting fresh supply air (outside air) 28 into the inlet plenum 24.

The supply plenum 26 has a supply port 31 for discharging air 29, which has passed through the heat exchanger 6 from the heat recovery ventilator 1 into an enclosure or dwelling. The discharge plenum 40 has an exhaust port 33 for discharging exhaust air 37 from the discharge plenum 40. The exhaust plenum 34 has an exhaust inlet port 35 for admitting warm air 38 from an enclosure or dwelling into the exhaust plenum 34. It will, however, be understood that external fans (not shown) might also be connected to the exhaust inlet port 35 and the intake port 30 to assist in augmenting air flow along the inlet passageway 20 and outlet passageway 36.

A non-motorized bypass section (flap) 42 separates the inlet plenum 24 and the exhaust plenum 34, and, when the bypass section (flap) 42 is opened, provides fluid flow and communication therebetween, in a discharge mode. As noted previously, the heat recovery ventilator utilizes a non-motorized, passive bypass section (flap) 42 to introduce warm air to both channels of the heat exchanger 6, so as to accelerate defrost, continue some ventilation of stale warm air, and recirculate a portion of the stale air flow, so as to warm incoming cold fresh air. In the present invention, because the air is under a negative pressure, the air being bypassed is being sucked back into the dwelling, thus reducing the net stale air exhausted to the outdoors. With further reference to FIG. 3, when heat recovery ventilator 1 is in its ventilation mode, warm moist air from a dwelling is replaced with fresh outside air, while, at the same time, recovering the heat from the warm moist air to be expelled and transferring it to the incoming fresh outside air, while at the same time accelerating defrosting of the heat exchanger 6. Of course, the transfer of heat to the incoming fresh air will cause condensation on the heat exchanger, which will accumulate, thus requiring defrosting of the heat exchanger 6.

As noted above, the air being exhausted (by way of the exhaust fan) through the exhaust plenum 34 is under a negative pressure, so the stale air will still be sucked out, and fresh air drawn in, even when the fresh air supply fan is not on (such as during defrost mode). In the embodiment of the present invention shown in FIG. 3, warm exhaust air 38 to be expelled enters the exhaust inlet port 35 and into the exhaust plenum 34. Because the air being exhausted (by way of the exhaust fan) through the exhaust plenum 34 is under a negative pressure, the stale air will still be sucked out through exhaust passageway 36 into discharge plenum 40 (along flow path 77 in FIG. 3 and which is also indicated as flow path AB@ in FIG. 5), but also through the passive non-motorized bypass section (flap) 3 (which move to allow the air flow therethrough under the negative pressure) into inlet plenum 24 (along flow path 79 in FIG. 3 and which is also indicated as flow path AA@ in FIG. 5). Further, because fresh air continues to be drawn into inlet plenum 24, due to the negative pressure, the warm stale air which has passed through the bypass section (flap) 42 into inlet plenum 24 is then drawn through the heat exchanger 6 along the inlet passageway 20 into supply plenum 26, and out through supply port 31 into the enclosure or dwelling. With reference to FIGS. 3, 5, 6 and 7, it can be seen that two independent air flows are introduced in both channels of the heat exchanger 6, so as to accelerate defrost, continue some ventilation of stale warm air, and recirculate a portion of the stale air flow at mild temperatures as opposed to the lower temperatures of incoming fresh air. During normal ventilation (that being, when the fresh air supply motor is engaged after the defrost mode), the static pressure then created by air moving through the fresh air passages in the heat exchanger creates more of a pressure drop than the strait air passages on the stale air side. Thus, this differential pressure is used to then close off the bypass section (flap).

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A heat recovery ventilator comprising: a heat exchanger having discrete inlet and exhaust passageways extending therethrough for providing heat transfer and flow between respective fluids flowing along said inlet and said exhaust passageways, said inlet passageway providing fluid communication between an inlet plenum and a supply plenum, said exhaust passageway providing fluid communication between an exhaust plenum and an exhaust discharge plenum; and a bypass section positioned between said inlet plenum and said exhaust plenum, the bypass section being movable between a venting configuration, in which the bypass section is in a closed position for allowing fluid communication between the exhaust plenum and the exhaust discharge plenum, and a defrost configuration, in which the bypass section is in an open position and permits fluid communication between said inlet plenum and said exhaust plenum, in addition to allowing fluid communication between the exhaust plenum and the exhaust discharge plenum.
 2. The heat recovery ventilator of claim 1, wherein the inlet plenum further comprises an inlet port for admitting supply air into said inlet plenum.
 3. The heat recovery ventilator of claim 1, wherein the supply plenum further comprises a supply port for discharging supply air from the supply plenum.
 4. The heat recovery ventilator of claim 1, wherein the exhaust plenum further comprises an exhaust inlet port for admitting exhaust air into the exhaust plenum.
 5. The heat recovery ventilator of claim 1, wherein the exhaust discharge plenum further comprises an exhaust port for discharging exhaust air from the exhaust discharge plenum.
 6. A heat recovery ventilator comprising a heat exchanger having discrete inlet and exhaust passageways extending therethrough for providing heat transfer and flow between respective fluids flowing along said inlet and said exhaust passageways, said inlet passageway providing fluid communication between an inlet plenum having an inlet port for admitting supply air into said inlet plenum and a supply plenum having a supply port for discharging supply air, said exhaust passageway providing fluid communication between an exhaust plenum having an exhaust inlet port and an exhaust discharge plenum, said exhaust discharge plenum having an exhaust port for discharging exhaust air from said exhaust discharge plenum; and a bypass section positioned between said inlet plenum and said exhaust plenum, the bypass section being movable between a venting configuration, in which the bypass section is in a closed position for allowing fluid communication between the exhaust plenum and the exhaust discharge plenum, and a defrost configuration, in which the bypass section is in an open position and permits fluid communication between said inlet plenum and said exhaust plenum, in addition to allowing fluid communication between the exhaust plenum and the exhaust discharge plenum.
 7. A heat recovery ventilator of claim 6, wherein any of the said inlet passageway and exhaust passageway includes a plurality of individual adjacent passageways.
 8. A heat recovery ventilator of claim 6, wherein the supply inlet plenum, the supply discharge plenum, the exhaust inlet plenum and the exhaust discharge plenum are at least partially defined by a housing containing the heat exchanger.
 9. A heat recovery ventilator of claim 6, wherein either the fluid flow along the exhaust passageway is augmented by an exhaust fan mounted within one of the exhaust plenum and the exhaust discharge plenum or the fluid flow along said inlet passageway is augmented by a supply fan mounted within the inlet plenum.
 10. A heat recovery ventilator of claims 6, wherein both the fluid flow along the exhaust passageway is augmented by an exhaust fan mounted within one of the exhaust plenum and the exhaust discharge plenum and the fluid flow along said inlet passageway is augmented by a supply fan mounted within the inlet plenum.
 11. A heat recovery ventilator of claim 10, wherein the exhaust fan and the supply fan are of similar capacity.
 12. A heat recovery ventilator as claimed in claim 11, wherein the exhaust fan and the supply fan share a common fan motor.
 13. A heat recovery ventilator comprising: a heat exchanger having discrete inlet and exhaust passageways extending therethrough for providing heat transfer and flow between respective fluids flowing along said inlet and said exhaust passageways, said inlet passageway providing fluid communication between an inlet plenum having an inlet port for admitting supply air into said inlet plenum and a supply plenum having a supply port for discharging supply air, said exhaust passageway providing fluid communication between an exhaust plenum having an exhaust inlet port and an exhaust discharge plenum, said exhaust discharge plenum having an exhaust port for discharging exhaust air from said exhaust discharge plenum; a supply fan mounted within the inlet plenum for augmenting fluid flow along said inlet passageway; an exhaust fan mounted within one of the exhaust plenum and the exhaust discharge plenum for augmenting fluid flow along the exhaust passageway; and a bypass section positioned between said inlet plenum and said exhaust plenum, the bypass section being movable between a venting configuration, in which the supply fan is turned on and the bypass section assumes a closed position for allowing fluid communication between the exhaust plenum and the exhaust discharge plenum, and a defrost configuration, in which the supply fan is turned off and the bypass section assumes an open position and permits fluid communication between said inlet plenum and said exhaust plenum, in addition to allowing fluid communication between the exhaust plenum and the exhaust discharge plenum.
 14. The heat recovery ventilator as claimed in claim 13, wherein, when the supply fan is turned off during the defrost configuration, the exhaust air being exhausted through the exhaust plenum is under a positive pressure, and, as a result of the positive pressure, the exhaust air continues to be drawn out while supply air continues to be drawn in to the inlet plenum.
 15. The heat recovery ventilator as claimed in claim 14, wherein, when the supply fan is turned on during the venting configuration, static pressure is created by supply air moving through the inlet passageway in the heat exchanger, and the static pressure creates a greater pressure drop than static pressure created by exhaust air moving through the exhaust passageway in the heat exchanger, which moves the bypass section to assume the closed position.
 16. The heat recovery ventilator as claimed in claim 14, wherein the bypass section is a passive, non-motorized damper. 